Programming Support to Enhance SEER Data with Data from the Center for Medicare and Medicaid Services-The National Cancer Institute (NCI) sponsors the Surveillance, Epidemiology and End Results (SEER) program, which includes 18 cancer registries that work under contract to report uniform data on all incident cancer cases in their defined geographic areas. The program covers about 28% of the U.S. population. For a number of years, NCI has participated in the enhancement of the SEER data with information available from the Center for Medicare and Medicaid Services (CMS). The enhancement has entailed matching patients included in the SEER cancer registry data with three different data resources at CMS?Medicare?s master enrollment file; the Medicare claims for health care provided to beneficiaries, and the Medicare Health Outcomes Survey (MHOS), which contains survey data related to the health-related quality of life for Medicare HMO enrollees. Augmenting the SEER data with these additional data sources has significantly expanded the range of research projects that can be performed. It has resulted in greater understanding of the types and quality of care provided to elderly cancer patients.